Implantable medical devices such as pacemakers and cardiac defibrillators often employ leads that are used to provide therapy to a patient and/or to sense various parameters within a patient's body. An implantable cardiac defibrillator lead, for example, may include a flexible lead body tube containing a number of exposed electrodes for providing stimulus energy to a desired location within the patient's heart. In some cases, an outer tube may be placed over portions of the lead body to provide the lead with a desired physical characteristic during implantation of the lead within the body. In implantation techniques using a hemostatic introducer to percutaneously insert the lead into the body, for example, an outer tube placed over the lead body can be used to facilitate insertion and subsequent removal of the lead within the interior lumen of the introducer.
In some designs, the various components of the lead, including the lead body tube and outer tube, are fabricated using a number of polymeric members that are assembled together and bonded to each other during manufacturing. Typically, the polymeric materials used in the construction of the lead are selected so as to meet various design specifications, including lead flexibility, radial and longitudinal strength, reliability, and biocompatibility. In some cases, more than one polymeric material is used to provide the desired combination of lead properties.
A number of different techniques have been employed for bonding polymeric and other lead members together, including adhesive bonding, thermal bonding, and chemical bonding. Many of these techniques, however, require specific material combinations, and in some cases can result in a change in the desired physical characteristics of the lead itself. In an adhesive technique, for example, the adhesives used may have limitations regarding the substrate combinations that can be bonded together, and may require additional steps such as the use of primers or surface activation to achieve reliable bonding. Another issue with adhesive techniques is that the application area of the adhesive may be limited. In some cases, for example, the adhesive bonds may be formed at only certain locations along the length of the lead, which can cause bunching between the outer tube and the lead body. Such bunching can occur, for example, when the lead is inserted into and subsequently removed from the introducer used for inserting the lead into the body, which exerts a force on the outer tube that causes the outer tube to move relative to the lead body tube. In some cases, the bunching can result in increased stress on the adhesive bonds between the outer tube and the lead body tube as well as increased stress on other bonds such as those used to secure the electrodes to the lead body tube.